Qt Test Overview

Qt Test is a framework for unit testing Qt based applications and libraries. Qt Test provides all the functionality commonly found in unit testing frameworks as well as extensions for testing graphical user interfaces.

Qt Test is designed to ease the writing of unit tests for Qt based applications and libraries:

LightweightQt Test consists of about 6000 lines of code and 60 exported symbols.
Self-containedQt Test requires only a few symbols from the Qt Core module for non-gui testing.
Rapid testingQt Test needs no special test-runners; no special registration for tests.
Data-driven testingA test can be executed multiple times with different test data.
Basic GUI testingQt Test offers functionality for mouse and keyboard simulation.
BenchmarkingQt Test supports benchmarking and provides several measurement back-ends.
IDE friendlyQt Test outputs messages that can be interpreted by Visual Studio and KDevelop.
Thread-safetyThe error reporting is thread safe and atomic.
Type-safetyExtensive use of templates prevent errors introduced by implicit type casting.
Easily extendableCustom types can easily be added to the test data and test output.

Creating a Test

To create a test, subclass QObject and add one or more private slots to it. Each private slot is a test function in your test. QTest::qExec() can be used to execute all test functions in the test object.

In addition, there are four private slots that are not treated as test functions. They will be executed by the testing framework and can be used to initialize and clean up either the entire test or the current test function.

  • initTestCase() will be called before the first test function is executed.
  • cleanupTestCase() will be called after the last test function was executed.
  • init() will be called before each test function is executed.
  • cleanup() will be called after every test function.

If initTestCase() fails, no test function will be executed. If init() fails, the following test function will not be executed, the test will proceed to the next test function.


class MyFirstTest: public QObject
private slots:
    void initTestCase()
    { qDebug("called before everything else"); }
    void myFirstTest()
    { QVERIFY(1 == 1); }
    void mySecondTest()
    { QVERIFY(1 != 2); }
    void cleanupTestCase()
    { qDebug("called after myFirstTest and mySecondTest"); }

For more examples, refer to the Qt Test Tutorial.

Building a Test

If you are using qmake as your build tool, just add the following to your project file:

QT += testlib

If you would like to run the test via make check, add the additional line:

CONFIG += testcase

See the qmake manual for more information about make check.

If you are using other build tools, make sure that you add the location of the Qt Test header files to your include path (usually include/QtTest under your Qt installation directory). If you are using a release build of Qt, link your test to the QtTest library. For debug builds, use QtTest_debug.

See Writing a Unit Test for a step by step explanation.

Qt Test Command Line Arguments


The syntax to execute an autotest takes the following simple form:

testname [options] [testfunctions[:testdata]]...

Substitute testname with the name of your executable. testfunctions can contain names of test functions to be executed. If no testfunctions are passed, all tests are run. If you append the name of an entry in testdata, the test function will be run only with that test data.

For example:

/myTestDirectory$ testQString toUpper

Runs the test function called toUpper with all available test data.

/myTestDirectory$ testQString toUpper toInt:zero

Runs the toUpper test function with all available test data, and the toInt test function with the test data called zero (if the specified test data doesn't exist, the associated test will fail).

/myTestDirectory$ testMyWidget -vs -eventdelay 500

Runs the testMyWidget function test, outputs every signal emission and waits 500 milliseconds after each simulated mouse/keyboard event.


Logging Options

The following command line options determine how test results are reported:

  • -o filename,format
    Writes output to the specified file, in the specified format (one of txt, xml, lightxml or xunitxml). The special filename - may be used to log to standard output.
  • -o filename
    Writes output to the specified file.
  • -txt
    Outputs results in plain text.
  • -xml
    Outputs results as an XML document.
  • -lightxml
    Outputs results as a stream of XML tags.
  • -xunitxml
    Outputs results as an Xunit XML document.
  • -csv
    Outputs results as comma-separated values (CSV). This mode is only suitable for benchmarks, since it suppresses normal pass/fail messages.
  • -teamcity
    Outputs results in TeamCity format.

The first version of the -o option may be repeated in order to log test results in multiple formats, but no more than one instance of this option can log test results to standard output.

If the first version of the -o option is used, neither the second version of the -o option nor the -txt, -xml, -lightxml, -teamcity or -xunitxml options should be used.

If neither version of the -o option is used, test results will be logged to standard output. If no format option is used, test results will be logged in plain text.

Test Log Detail Options

The following command line options control how much detail is reported in test logs:

  • -silent
    Silent output; only shows fatal errors, test failures and minimal status messages.
  • -v1
    Verbose output; shows when each test function is entered. (This option only affects plain text output.)
  • -v2
    Extended verbose output; shows each QCOMPARE() and QVERIFY(). (This option affects all output formats and implies -v1 for plain text output.)
  • -vs
    Shows all signals that get emitted and the slot invocations resulting from those signals. (This option affects all output formats.)

Testing Options

The following command-line options influence how tests are run:

  • -functions
    Outputs all test functions available in the test, then quits.
  • -datatags
    Outputs all data tags available in the test. A global data tag is preceded by ' __global__ '.
  • -eventdelay ms
    If no delay is specified for keyboard or mouse simulation (QTest::keyClick(), QTest::mouseClick() etc.), the value from this parameter (in milliseconds) is substituted.
  • -keydelay ms
    Like -eventdelay, but only influences keyboard simulation and not mouse simulation.
  • -mousedelay ms
    Like -eventdelay, but only influences mouse simulation and not keyboard simulation.
  • -maxwarnings number
    Sets the maximum number of warnings to output. 0 for unlimited, defaults to 2000.
  • -nocrashhandler
    Disables the crash handler on Unix platforms. On Windows, it re-enables the Windows Error Reporting dialog, which is turned off by default. This is useful for debugging crashes.
  • -platform name
    This command line argument applies to all Qt applications, but might be especially useful in the context of auto-testing. By using the "offscreen" platform plugin (-platform offscreen) it's possible to have tests that use QWidget or QWindow run without showing anything on the screen. Currently the offscreen platform plugin is only fully supported on X11.

Benchmarking Options

The following command line options control benchmark testing:

  • -callgrind
    Uses Callgrind to time benchmarks (Linux only).
  • -tickcounter
    Uses CPU tick counters to time benchmarks.
  • -eventcounter
    Counts events received during benchmarks.
  • -minimumvalue n
    Sets the minimum acceptable measurement value.
  • -minimumtotal n
    Sets the minimum acceptable total for repeated executions of a test function.
  • -iterations n
    Sets the number of accumulation iterations.
  • -median n
    Sets the number of median iterations.
  • -vb
    Outputs verbose benchmarking information.

Miscellaneous Options

  • -help
    Outputs the possible command line arguments and gives some useful help.

Creating a Benchmark

To create a benchmark, follow the instructions for creating a test and then add a QBENCHMARK macro to the test function that you want to benchmark.

class MyFirstBenchmark: public QObject
private slots:
    void myFirstBenchmark()
        QString string1;
        QString string2;
        QBENCHMARK {

The code inside the QBENCHMARK macro will be measured, and possibly also repeated several times in order to get an accurate measurement. This depends on the selected measurement back-end. Several back-ends are available. They can be selected on the command line:

NameCommand-line ArgumentAvailability
Walltime(default)All platforms
CPU tick counter-tickcounterWindows, macOS, Linux, many UNIX-like systems.
Event Counter-eventcounterAll platforms
Valgrind Callgrind-callgrindLinux (if installed)
Linux Perf-perfLinux

In short, walltime is always available but requires many repetitions to get a useful result. Tick counters are usually available and can provide results with fewer repetitions, but can be susceptible to CPU frequency scaling issues. Valgrind provides exact results, but does not take I/O waits into account, and is only available on a limited number of platforms. Event counting is available on all platforms and it provides the number of events that were received by the event loop before they are sent to their corresponding targets (this might include non-Qt events).

The Linux Performance Monitoring solution is available only on Linux and provides many different counters, which can be selected by passing an additional option -perfcounter countername, such as -perfcounter cache-misses, -perfcounter branch-misses, or -perfcounter l1d-load-misses. The default counter is cpu-cycles. The full list of counters can be obtained by running any benchmark executable with the option -perfcounterlist.

  • Notes:
    • Using the performance counter may require enabling access to non-privileged applications.
    • Devices that do not support high-resolution timers default to one-millisecond granularity.

See Writing a Benchmark in the Qt Test Tutorial for more benchmarking examples.

3rd Party Code

The CPU tick counters used for benchmarking are licensed under the following license: (from src/testlib/3rdparty/cycle.h)

Copyright (c) 2003, 2006 Matteo Frigo
Copyright (c) 2003, 2006 Massachusetts Institute of Technology

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.


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